Mosquito fish (see also 'Gambusia') are used in ponds to control mosquitoes. Mosquitoes breed in standing water where there is little turbulence. It is important as a pond owner to do whatever you can to impede the population of mosquitoes, and to slow the spread of West Nile virus. Did you know that you can't get West Nile from mosquitoes that bite during the day? Only the dusk till dawn biters carry it. The Mosquito Abatement District will come out to your place and help you control mosquitoes for free (actually, you've already paid for the service with you taxes,) and they would love to do it, because they want to keep them under control. They can't go into people's yards without their permission, and that's where a lot of mosquitoes come from. They will bring you mosquito fish or pellets, depending on where you live and what you want. And here's an interesting fact--it's actually illegal to get mosquito fish (Gambusia) from anywhere but the Mosquito Abatement District. The Department of Fish and Game tried to exterminate them because there were so many, and were going to outlaw them altogether. Gambusia are not native to Utah. Someone brought over a hand full back in the mid 19oo's and now you can hardly find a body of water in this state that doesn't have them!

The following is an excerpt from Utah Water Gardens previous website:

Gambusia are a minnow-type fish that mosquito abatement uses to control the mosquito. They are small, ranging in size from .5-3 inches with the females being much larger than the males. There is no remarkable coloration of the fish. Gambusia use in ornamental ponds and large bird baths gave similar results to Gambusia use in swimming pools. Because of size and nutrient limitations, only limited fish reproduction was observed. Between 15 and 50 fish should be stocked, depending on the size of the pond. In ornamental ponds containing other fish, check for mosquito larvae before introducing Gambusia because the fish already present could be effectively controlling the mosquito larvae. They will also eat frog tadpoles and other small fish fry. Due to winter die off in most ornamental pond situations, Gambusia will need to be stocked on a yearly basis. Mosquito fish are rather aggressive, and not just toward other fishes, but also toward each other. Quite often the fins turn up ragged. Probably in part due to their being extremely well adapted to a rough life. There are a number of resent studies that question the effectiveness of this fish to control mosquitoes. It is reported that Guppies do a good job as well.